Adaptation of the small intestine--does it occur in man?

After resection and usually after shunt operations for obesity, the small bowel in-situ or in-continuity develops mucosal hyperplasia and enhanced absorption per unit length of intestine in animals and man, although the studies in man are limited. The opposite occurs in the small bowel deprived of food either by bypass or total parenteral nutrition (TPN). The changes which occur in the bypassed bowel are not consistent and cannot be explained by the luminal nutrition theory alone. The effect of TPN on jejunal function has been assessed in preterm infants using the one hour blood xylose test and potential difference changes after the infusion of glucose. The results of these tests suggest that the absorptive surface area is diminished during TPN, increases following enteral feeding, and is not related to post-natal age. Function at a cellular level probably remains constant. The mechanism of adaptation is poorly defined in man, but animal studies suggest that in addition to luminal nutrition, other factors such as hormones, and pancreatico-biliary secretions, are important but that there is a fine balance of agonists and antagonists.